It communicates with Oracle Services for Microsoft Transaction Server to enlist the Oracle Database in transactions started by MS DTC.

The MTS-based COM components can acquire connections to both dedicated and shared Oracle servers of a database. The components can then attempt to perform distributed updates, using data manipulation language, on another database using pre-existing database links between these databases. While the distributed updates from shared servers succeed, those from dedicated servers fail.

Registry parameters that handle tracing are automatically set in \\HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\HOMEID during the installation of Oracle Services for Microsoft Transaction Server. Use the registry parameters instead of setting them as environment variables; setting environment variables requires you to restart your computer for the changes to occur.

7.2 Correcting Windows Explorer Problems

If you are using Windows and experience Windows Explorer crashes or other unexpected Windows problems when using Microsoft Transaction Server with a database, install the Windows 4.0 Service Pack 6a or greater (available from Microsoft).

7.3 Correcting Oracle Net Changes that Impact Connection Pooling

The connection pool provided by the OraMTS layer, oramts.dll, uses a connection's net service name to identify pooled connections for an application. If changes are made to the net service name, and pooled connections are available, the application using the connection pool must be stopped and restarted. These changes can include altering the host or the database system identifier (SID) for the net service name in the tnsnames.ora file.

These changes ensure that all currently pooled connections corresponding to the old net service name are destroyed and any new pooled connections use the changes made to the net service name. This includes any application hosting Microsoft Transaction Server components.

To empty connection pools, perform the following:

If the application is an out-of-process Microsoft Transaction Server component (server package), run the following application:

C:\> mtxstop

This empties the connection pools.

If the application is an in-process Microsoft Transaction Server component (library package), terminate the application. This also empties the connection pool.

7.4 Designing an Application that Uses Multiple Databases

Oracle clients can establish connections to a database in two ways:

Typical Oracle clients establish connections to a database using a dedicated server configuration. In a dedicated server configuration, one client corresponds to one Oracle server process.

For scalability under heavy loads, Oracle clients have the option of using a shared server configuration. In a shared server configuration, a single Oracle server process can be shared by more than one client connection.

Microsoft Transaction Server communicates with the database through distributed transactions. In a dedicated server configuration, you cannot use distributed updates (data manipulation language statements across database links) from other databases. However, if the original connection to the database is established using shared server configurations, the distributed updates from other databases succeed.

To use data manipulation language statements in shared server configurations, set the following parameter in the tnsnames.ora file:

SERVER=dedicated

This forces the Oracle Net listener to provide a dedicated connection. Figure 7-1 shows this process.

7.5 Working with Different Types of Connection Pooling

Oracle Net Connection Pooling Oracle Net connection pooling is a server-side feature that is implemented only if the Oracle Database is configured for shared server support. Oracle Net connection pooling enables you to minimize the number of physical network connections to a shared server. This is achieved by sharing a dispatcher's set of connections among multiple client processes.

7.6 Working with In-Doubt Transactions

Distributed database configurations, such as distributed updates using database links

External transaction managers, such as Tuxedo and MS DTC, for coordinating transaction outcome

The two-phase commit protocol completes these transactions. During phase one, the transaction manager (TM) requests the various resource managers involved in the TM's transaction to prepare the underlying distributed transactions. In phase two, the TM determines whether it commits or terminates the transaction, and requests the resource managers to commit or terminate the underlying transaction. If a resource manager fails to receive the phase two notification, the underlying distributed transaction becomes in-doubt.

To integrate Oracle with Microsoft Transaction Server, distributed transactions are used in the database. Distributed transactions correspond to transactions coordinated by the MS DTC. A distributed transaction can become in-doubt when the transaction cannot commit or terminate (phase two of the two-phase commit). This occurs when the Microsoft Transaction Server application server process, database, or network fails.

The Microsoft Transaction Server administrative user account is created by running the oramtsadmin.sql script. If you later change the database with which Microsoft Transaction Server is coordinating transactions, you can drop the administrative user account schema from the previous database.

To drop the Microsoft Transaction Server administrative user account:

Start SQL*Plus:

c:\> sqlplus /NOLOG

Connect to the database as SYSDBA:

SQL> CONNECT / AS SYSDBA

Enter the following command to drop administrative user account schema:

SQL> DROP USER mtsadmin_username CASCADE;

where mtsadmin_username is the Microsoft Transaction Server administrative user account (default is mtssys).